Various thermoplastic resins have recently been attracting more and more attention as matrix materials for composite materials reinforced with long fibers, because such thermoplastic resins have many advantages as matrix materials over thermosetting resins employed conventionally as principal matrix materials because of the realization of reuse of scraps and post processing, the elimination of the need for shelf-life control, substantially-shortened processing cycles, and improved moisture resistance.
With the recent advancement of weight-reducing technology in the fields of the aircraft, space, automobile, electrical and electronic, and other industries, development of composite materials reinforced with long fibers, ACM (Advanced Composite Materials), has been proceeded with rapidly. Conventionally, they primarily contained a thermosetting resin as a matrix material. There is however a growing demand for the development of matrix materials composed of a thermoplastic resin in order to meet desires for the possibility of reuse of scraps and post processing, the elimination of shelf-life control, the shortening of processing cycles and the improvement of moisture resistance. In the above-mentioned industrial fields in particular, there has been a particular demand for thermoplastic resins which as matrix materials, have heat resistance of about 300.degree. C. or higher in terms of melting point and crystallinity facilitating melt forming or molding and processing.
As crystalline, heat-resistant, thermoplastic resins developed to date, there are, for example, poly(butylene terephthalate), polyacetal, poly(p-phenylene thioether), etc. These resins are however unable to meet the recent requirement level for heat resistance.
Polyether ether ketone (hereinafter abbreviated as "PEEK") and polyether ketone (hereinafter abbreviated as "PEK") have recently been developed as heat-resistant resins. These resins have a melting point of about 300.degree. C. or higher and moreover, they are crystalline thermoplastic resins. It is possible to form or mold heat-resistant high-performance composite products from prepregs making use of such a resin as a matrix material.
PEEK and PEK however use expensive fluorine-substituted aromatic compounds as their raw materials. They hence involve such problems that they are costly and their use is limited for economical reasons.
Based on an assumption that PTK could be a promising candidate for heat-resistant thermoplastic resin like PEEK and PEK owing to their similarity in chemical structure, PTK has been studied to some extent to date.
There are some disclosure on PTKs, for example, in German Offenlegungsschrift 34 05 523Al (hereinafter abbreviated as "Publication A"), Japanese Patent Laid-Open No. 58435/1985 (hereinafter abbreviated as "Publication B"), Japanese Patent Laid-Open No. 104126/1985 (hereinafter abbreviated as "Publication C"), Japanese Patent Laid-Open No. 13347/1972 (hereinafter abbreviated as "Publication D"), Indian J. Chem., 21A, 501-502 (May, 1982) (hereinafter abbreviated as "Publication E"), Japanese Patent Laid-Open No. 221229/1986 (hereinafter abbreviated as "Publication F"), and German Offenlegungsschrift 34 29 670Al (hereinafter abbreviated as "Publication G").
It has however been difficult to provide a substantially defect-free, formed or molded product having a high density, high mechanical properties and high heat resistance, such as that required in the field of the aircraft industry, and the like, even if prepregs are formed using as a matrix material any one of the PTKs described in these publications. This is attributed to the fact that the PTKs developed so far have poor melt stability and undergo a crosslinking reaction, which is accompanied by a loss of crystallinity and an increase in melt viscosity, or foaming whereby they can hardly be filled thoroughly in a molten state into every corner of a fibrous reinforcing material.
Since the conventional PTKs are all insufficient in melt stability as described above, it has still been unable to obtain substantially defect-free, molded or formed products of high density, high mechanical properties and high heat resistance required in industrial fields such as the aircraft industry and space industry.